Performance improvement of low pressure turbine blade by using synthetic jets

In order to investigate the effect of flow separation control using synthetic jets on the performance of a low pressure turbine (LPT) blade, the three-dimensional viscous unsteady Reynolds-averaged Navier-Stokes equations are solved to predict the unsteady flow characteristics of the LPT Pak-B blade with and without synthetic jets. For turbulent flow, shear stress transport (SST) turbulence model coupled with Langtry-Menter transition model is adopted. The numerical results show that the turbulence simulations can describe the flow structure effectively and capture the flow separation and reattachment locations on the suction surface of the Pak-B blade. At low Reynolds numbers, using synthetic jet can effectively suppress or even eliminate the flow separation on the blade suction surface. At Re=25,000 and freestream turbulence intensity FSTI=0.08%, there is a synthetic jet frequency in the range from 0Hz to 50Hz for optimal flow control of the LPT blade. The total pressure loss of the LPT blade decreases by 59%, compared with that of non-synthetic jet blade at the blowing ratio B=2.0 and the optimal jet frequency f=20Hz. In addition, the flow control mechanism of synthetic jets is revealed in detail. A hysteresis is observed in the process of flow control by using synthetic jets to reattach the blade boundary layer flow separation. The hysteresis in the blowing process of synthetic jets and the acquirement of enough time to restrain the separation in the sucking process are the main factors which affect the selection of synthetic jet frequency.